1. Field of the Invention
The present invention relates to a control apparatus for a clutch disposed between an engine and a gear transmission on an automobile, and more particularly to a clutch control apparatus for disengaging a clutch in order to prevent an engine from being forcibly stopped when a brake is operated.
2. Description of the Prior Art
Automatic clutch control apparatus have been used in recent years for controlling the operation of a clutch between an engine and a gear transmission on an automobile based on operating conditions of the automobile such as the rotational speed of the engine and the amount of depression of an accelerator pedal.
While the automobile with such an automatic clutch control apparatus is running, the driver may abruptly brake the automobile in case of emergency. If the wheels are stopped while the clutch remains engaged, an excessive load is imposed on the engine causing the engine to stop its operation. To prevent the engine from being shut off under such a condition, there has been proposed an automatic clutch control method for disengaging the clutch when the automobile is abruptly braked by detecting that the deceleration of the automobile is larger than a certain deceleration limit (see Japanese Laid-Open Patent Publication No. 60-8553).
The applicant has proposed a clutch control system wherein a clutch is disengaged on the basis of a detected signal supplied from an automobile braking force detecting means to an electronic controller (see Japanese Patent Application No. 60-205801.)
In the above proposals, various preset and integrated values based on which clutch disengagement is controlled are common values without any concern over transmission gear positions. Therefore, in lower gear positions, the clutch tends to be disengaged too early to utilize effective engine braking, and in higher gear positions, the clutch tends to be disengaged too late, inviting a forced engine stop.
With a clutch control system for use on large-size automobiles, air is present in a brake pipe system to exert a weak braking force at an initial stage and then an abruptly strong braking force at a later stage when the brake is suddenly applied. This characteristic is disadvantageous in that the timing to detect when the wheels are about to lock is apt to be delayed, resulting in the possibility of a forced engine stop.